Exhaust system

Abstract

An exhaust system (1) is provided with an exhaust passage that allows exhaust gas discharged from an internal combustion engine to pass therethrough, an exhaust emission control unit including a catalyst (2,3) such as a three-way catalyst (27) to purify the exhaust gas, and an exhaust heat collecting unit that converts thermal energy of the exhaust gas into electric energy. The exhaust passage (25) is formed in the center of the exhaust system provided with the exhaust emission control unit. By-pass passages (26) are formed at both sides of the exhaust passage (25) through which the exhaust gas flows without passing through the exhaust emission control unit. The exhaust heat collecting unit (29) is provided on the outer side of each of the by-pass passages (26).

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of Invention [0002] The invention relates to an exhaust system that purifies exhaust gas using catalyst and converts thermal energy of the exhaust gas into electric energy. [0003] 2. Description of Related Art [0004] Generally, an exhaust system includes an exhaust emission catalyst such as a three-way catalyst to purify exhaust gas discharged from an engine by removing hazardous substance contained in the exhaust gas, for example, carbon monoxide, hydrocarbon, nitrogen oxides and the like. The catalyst becomes effective to purify the exhaust gas when it is activated at its activated temperature in the range between 350° C. and 800° C., for example. [0005] Substantially high thermal energy of the exhaust gas at a high temperature is partially used for increasing the temperature of the exhaust emission catalyst until it reaches the activated temperature. The rest of the thermal energy of the exhaust gas, however, is dispersed without being ...

AI Technical Summary

Benefits of technology

[0009] It is an object of the invention to provide an exhaust system that prevents degradation of the catalyst while improving the fuel efficiency.

[0010] The exhaust system according to one aspect of the invention includes a primary exhaust emission control unit for purifying the exhaust gas and a first exhaust heat collecting unit for collecting the thermal energy through conversion thereof into electric energy. The exhaust system includes a second passage through which the exhaust gas flows without passing through the primary exhaust emission control unit in addition to the first passage that allows the exhaust gas to flow therethrough. The exhaust system includes the primary exhaust emission control unit within the first passage so as to purfy the exhaust gas flowing therethrough. The exhaust system includes a control member that serves to change a flow of gas between the first passage and the second passage. In the case where the catalytic temperature becomes high, the exhaust gas is controlled to flow through the second passage in the exhaust system so as to avoid excessive increase in the catalytic temperature owing to the exhaust gas at high temperature. This makes it possible to prevent thermal degradation in the catalyst. This may also eliminate the need for preventing the rise in the catalytic temperature by operating the engine in a fuel-rich state to decrease the exhaust gas temperature. Furthermore, the thermal energy of the exhaust gas can be collected as electric energy, resulting in improved fuel efficiency.

Problems solved by technology

The temperature of the exhaust gas passing at the position downstream of the exhaust catalyst, however, becomes low because it has been used for increasing the catalytic temperature or it has been dispersed as it flows, resulting in decrease in the thermal energy.

As a result, the thermoelectric conversion efficiency of the exhaust heat power generation apparatus is decreased, failing to effectively collect the thermal energy.

When the catalytic temperature exceeds the activated temperature, its purification effect is deteriorated, which may thermally degrade the catalyst.

This may increase the fuel supply quantity, resulting in deteriorated fuel efficiency.

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